iMac G3 mod - Video Connector

[rockyhill]

I made a small circuit to turn the CRT analog board on and off using the power button on the front.
Here is a video of it in action. Soon I'll put a schematic up.

 

[elvisa]

It is very much a struggle to find coherent documentation for all of this so I too am feeling a bit lost....
The VGA cable uses pins 12 & 15 as SDA and SCL respectively and you should be able to use any
of the grounds on the cable to hook into the pi

Many thanks for your doco Rocky. Watching your most recent video, it looks like the iMac you have might be the 33MHz model. I've only just realised the 333MHz model I'm attempting to use is radically different internally.

Rather than the J20 header, all that sticks out is an old style DB15 (two rows, rather than the 3 rows of a DE15 VGA cable) RGB cable.

You can see it in the iFixIt teardown here:

iMac G3 Model M4984 Logic Board Replacement

The iMac G3 (Tray-Loading) The iMac G3 was Apple's new G3 all-in-one. It had tons of new features, and removed all old interfaces. It was released...

www.ifixit.com

A better shot of where it connects to on the monitor's chassis is further down in this guide:

iMac G3 Model M4984 Power Supply Replacement

The iMac uses an incredibly hard to get to power supply. It has 24-Pins. This will require taking the iMac fully apart.

www.ifixit.com

iFixIt have some service manuals online. I'm going to dig through those and see if I can find anything that references the i2c pins (I suspect they're the "monitor sense" pins, but I just want to make sure):

iMac G3 Service Manual - iFixit

Repair your electronics yourself. iFixit is the repair manual you can edit. We sell tools, parts and upgrades for Apple Mac, iPod, iPhone, iPad, and MacBook as well as game consoles.

www.ifixit.com

 

[rockyhill]

Many thanks for your doco Rocky. Watching your most recent video, it looks like the iMac you have might be the 33MHz model. I've only just realised the 333MHz model I'm attempting to use is radically different internally.

Rather than the J20 header, all that sticks out is an old style DB15 (two rows, rather than the 3 rows of a DE15 VGA cable) RGB cable.

You can see it in the iFixIt teardown here:

iMac G3 Model M4984 Logic Board Replacement

The iMac G3 (Tray-Loading) The iMac G3 was Apple's new G3 all-in-one. It had tons of new features, and removed all old interfaces. It was released...

www.ifixit.com

A better shot of where it connects to on the monitor's chassis is further down in this guide:

iMac G3 Model M4984 Power Supply Replacement

The iMac uses an incredibly hard to get to power supply. It has 24-Pins. This will require taking the iMac fully apart.

www.ifixit.com

iFixIt have some service manuals online. I'm going to dig through those and see if I can find anything that references the i2c pins (I suspect they're the "monitor sense" pins, but I just want to make sure):

iMac G3 Service Manual - iFixit

Repair your electronics yourself. iFixit is the repair manual you can edit. We sell tools, parts and upgrades for Apple Mac, iPod, iPhone, iPad, and MacBook as well as game consoles.

www.ifixit.com

Oh Man, that is radically different!
I hope the IVAD init code is the same but if it isn't, you're probably going to have sniff the commands your self.
Maybe there's an i2c sniffer you can run directly on the pi. I'll look around and see.


I don't think it's a show stopper though.

 

[rockyhill]

I successfully powered the down converter board without the logic board. I think it can be used to power
an arduino, dvd drive, mini itx, ect... I have to experiment some more....

Here is a video where I measure some voltages.

 

[rockyhill]

Many thanks for your doco Rocky. Watching your most recent video, it looks like the iMac you have might be the 33MHz model. I've only just realised the 333MHz model I'm attempting to use is radically different internally.

Rather than the J20 header, all that sticks out is an old style DB15 (two rows, rather than the 3 rows of a DE15 VGA cable) RGB cable.

You can see it in the iFixIt teardown here:

iMac G3 Model M4984 Logic Board Replacement

The iMac G3 (Tray-Loading) The iMac G3 was Apple's new G3 all-in-one. It had tons of new features, and removed all old interfaces. It was released...

www.ifixit.com

A better shot of where it connects to on the monitor's chassis is further down in this guide:

iMac G3 Model M4984 Power Supply Replacement

The iMac uses an incredibly hard to get to power supply. It has 24-Pins. This will require taking the iMac fully apart.

www.ifixit.com

iFixIt have some service manuals online. I'm going to dig through those and see if I can find anything that references the i2c pins (I suspect they're the "monitor sense" pins, but I just want to make sure):

iMac G3 Service Manual - iFixit

Repair your electronics yourself. iFixit is the repair manual you can edit. We sell tools, parts and upgrades for Apple Mac, iPod, iPhone, iPad, and MacBook as well as game consoles.

www.ifixit.com

Hey Dan,

Searching for more pinouts,specifically the audio out board, I found this page. I think this is your model and there's a link for the pinout for the DB15.
Says "The video pinout is an exact old Apple video 15-pin pinout," http://old.pinouts.ru/Video/maclcvideo_pinout.shtml

I also think the monitor sense pins are the i2c lines.



BTW, Does your audio out board look like the one in this image. I think this is the one for my model based on what's left of my board.

[automerge]1581084955[/automerge]

Many thanks for your doco Rocky. Watching your most recent video, it looks like the iMac you have might be the 33MHz model. I've only just realised the 333MHz model I'm attempting to use is radically different internally.

Rather than the J20 header, all that sticks out is an old style DB15 (two rows, rather than the 3 rows of a DE15 VGA cable) RGB cable.

You can see it in the iFixIt teardown here:

iMac G3 Model M4984 Logic Board Replacement

The iMac G3 (Tray-Loading) The iMac G3 was Apple's new G3 all-in-one. It had tons of new features, and removed all old interfaces. It was released...

www.ifixit.com

A better shot of where it connects to on the monitor's chassis is further down in this guide:

iMac G3 Model M4984 Power Supply Replacement

The iMac uses an incredibly hard to get to power supply. It has 24-Pins. This will require taking the iMac fully apart.

www.ifixit.com

iFixIt have some service manuals online. I'm going to dig through those and see if I can find anything that references the i2c pins (I suspect they're the "monitor sense" pins, but I just want to make sure):

iMac G3 Service Manual - iFixit

Repair your electronics yourself. iFixit is the repair manual you can edit. We sell tools, parts and upgrades for Apple Mac, iPod, iPhone, iPad, and MacBook as well as game consoles.

www.ifixit.com

I just wanted to say that for years I've called the VGA connector a high density DB15, so I was a little confused
when you wrote DE15 but now I know that's the correct name. Gotta update stuff now.

 

[DrJekyll_XYZ]

Following this in waiting. People have been trying this from what i can see since around 2007. I have a imac g3 dv series with one of the best quality crt's that was available sat waiting to be gamed on. I obviously cant game on the mac but i can at least leverage its screen for my own evil plans.

 

[rockyhill]

Following this in waiting. People have been trying this from what i can see since around 2007. I have a imac g3 dv series with one of the best quality crt's that was available sat waiting to be gamed on. I obviously cant game on the mac but i can at least leverage its screen for my own evil plans.

Are you planning on using a raspberry pi or something a little more powerful?

 

[WhatDoYouGuysWannaDo]

Elvisa, on the tray loading iMac, you don't need to do any of this stuff. Just adapt the DB15 connector to regular VGA, and make sure you're sending a frequency that works, like 1024x768 @ 75Hz. I think it could benefit from injecting an EDID, but you don't need the SDA and SCL signals to turn on the display.

 

[DrJekyll_XYZ]

Are you planning on using a raspberry pi or something a little more powerful?

Well, i have an RPI sat in the wings running a retro setup so i can go that route.

I want to make this a little more universal though as an independent display without bastardizing the machine, i want to keep the imac working without damaging it (can buy second hand components to accomodate a switch for the monitor and an output port). They arent that cheap in the UK and take up a lot of space so having 2 may be a bit much.

Shouldnt the real goal be to succesfully run an xbox one or something on this thing? Find a way to convert the signal resolution and refresh rate in transit?

 

[rockyhill]

Elvisa, on the tray loading iMac, you don't need to do any of this stuff. Just adapt the DB15 connector to regular VGA, and make sure you're sending a frequency that works, like 1024x768 @ 75Hz. I think it could benefit from injecting an EDID, but you don't need the SDA and SCL signals to turn on the display.

Stephen, that will make life much simpler for Dan! I guess basically all one has to do in order to connect a raspberry pi to a slot loader is adapt the connector, as you said, and tweak the "/boot/config.txt"

I've searched a couple of times for pictures/documentation on your trayloader mod but I can't seem to find it. I'm very interested in seeing it, could you post a link?

 

[rockyhill]

Well, i have an RPI sat in the wings running a retro setup so i can go that route.

I want to make this a little more universal though as an independent display without bastardizing the machine, i want to keep the imac working without damaging it (can buy second hand components to accomodate a switch for the monitor and an output port). They arent that cheap in the UK and take up a lot of space so having 2 may be a bit much.

Shouldnt the real goal be to succesfully run an xbox one or something on this thing? Find a way to convert the signal resolution and refresh rate in transit?

Ultimately, what I would like, is to see is a solution where one can just remove the logic board and plug straight into
the existing connectors and use the CRT, speakers, power button ect....
Basically some adapter boards turning it into a stand alone VGA monitor.
This way one can always just unplug the boards and pop the original logic board right in and the iMac is back.

 

[DrJekyll_XYZ]

Ultimately, what I would like, is to see is a solution where one can just remove the logic board and plug straight into
the existing connectors and use the CRT, speakers, power button ect....
Basically some adapter boards turning it into a stand alone VGA monitor.
This way one can always just unplug the boards and pop the original logic board right in and the iMac is back.

I agree entirely that this would be great. Do we know where to get the connectors without snipping into cables. I imagine that for power we can use modern 20 pin atx power cable extensions that go to each side of a pcb so we dont need to splice wires for power or to drive an arduino. What are the exact connectors for the display as ive checked a few references and i cant find a name in order to make up non intrusive cables or just the socket so the video can be convert to VGA on the board while splitting to the arduino for edid and initialisation sequence. You can get pcb etch plans online for an arduino and and your own traces and mounting points.

Out of curiosity have you found a way to run the edid and initialisation on a single arduino?

 

[rockyhill]

I've looked around but I haven't been able to find the exact header that mates with the ones on the
chassis but I have found a couple with the same number of pins and with the same pitch.
With a slight modification to it's shroud, I was able to make a shrouded header mate with one of the
chassis connectors. In the end I think we'll be better off using a non shrouded header of the same pitch for this.

I've started putting together a schematic for one of the boards that plugs into the J20 connector.
What I had in mind was two atmega328p chips for this. One for the init sequence and one for the
EDID. So to answer your question, no I haven't found a way to use one arduino for both things. That
said, I really didn't try all that much and I probably will try some more once I've reassembled the iMac.

I had to change a capacitor and unfortunately I shattered the mounting posts that hold the CRT on the
inner bezel so I can't assemble the darn thing. I saved all of the shards and glued as much as I could
back together and used bondo to reinforce them. Then I added some drops of bicycle chain oil to the
posts and slowly worked the screws in to re-thread them.

I'm going to try and reassemble the iMac tomorrow lets see how it goes.

The reason I want to use two chips is because one will be powered by the iMac Analog board and
the other other via the VGA connector. The schematic is on github and you can use the latest version
of KiCad to view and edit it.
I still need to add a switch and some way to connect to the other PCB at J22 .
This could be with an atx power cable extension but I don't think we need that many wires but we still
have to look at it some more.

We don't need a complete arduino for this, just enough to get the chips going.
Here's a screen shot of what I have so far.

 

[pucher]

Hello, long time listener, first time commenter! Been following this thread for months and was excited to see a breakthrough, thank you for all of the work you have put into this! I have hooked my iMac up with a Raspberry Pi 4 and have been able to get everything going except for getting the actual screen on. I can load the init_ivad.py script through SSH and it will turn the screen on, but immediately turn off after about two seconds. Rebooting the Pi will also turn the screen on, but immediately turn it off as well. Nothing shows on the screen when it is on, but I can hear the "click". I have tried pressing keys on the Pi keyboard but it does not seem to be triggering the screen. Any idea what could be going on? Thanks again!

 

[rockyhill]

Hello, long time listener, first time commenter! Been following this thread for months and was excited to see a breakthrough, thank you for all of the work you have put into this! I have hooked my iMac up with a Raspberry Pi 4 and have been able to get everything going except for getting the actual screen on. I can load the init_ivad.py script through SSH and it will turn the screen on, but immediately turn off after about two seconds. Rebooting the Pi will also turn the screen on, but immediately turn it off as well. Nothing shows on the screen when it is on, but I can hear the "click". I have tried pressing keys on the Pi keyboard but it does not seem to be triggering the screen. Any idea what could be going on? Thanks again!

Sounds like your almost there!

A couple of questions just to make sure.

1 - Was the iMac working before you pulled the logic board?
2 - Are you jumpering pins 10 and 6 on the J20 connector ?
3 - Have you tested the HDMI to VGA converter separately with another monitor?
4 - Have you confirmed that the VGA cable is wired correctly? If you used the colors
I posted as a guide to splice into your cable make sure thye match up with the pins.
Apple might have changed the wire colors around to keep things lively.
5 - Did you add the lines to the /boot/config.txt file? Specifically
hdmi_group=2
hdmi_mode=18
6 - Do you have a raspberry pi 3 to test with before jumping to the RPI4?

I'm sure you did all of that but I just want to be thorough.

I did this with a Raspberry pi 3 so maybe the difference is there.

There might be an option or two that you'll need for the RPI 4 that I'm not aware of so read through the following.

https://www.raspberrypi.org/documentation/configuration/config-txt/video.md


I see you that you can specify which HDMI port to apply the options to.

Note for Raspberry Pi4B users: Because the Raspberry Pi 4B has two HDMI ports, some HDMI commands can be applied to either port. You can use the syntax <command>:<port>, where port is 0 or 1, to specify which port the setting should apply to. If no port is specified, the default is 0. If you specify a port number on a command that does not require a port number, the port is ignored. Further details on the syntax and alternatives mechanisms can be found on the conditionals page in the HDMI section of the documentation.

Here's a copy of the config.txt file from my pi , maybe I missed something. Let me know if you find that I missed
something and I'll add it to the instructions.

# For more options and information see
# http://rpf.io/configtxt
# Some settings may impact device functionality. See link above for details

# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1

# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
#disable_overscan=1

# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
#overscan_left=16
#overscan_right=16
#overscan_top=16
#overscan_bottom=16

# uncomment to force a console size. By default it will be display's size minus
# overscan.
#framebuffer_width=1280
#framebuffer_height=720

# uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
#hdmi_group=1
#hdmi_mode=1

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL
#sdtv_mode=2

#uncomment to overclock the arm. 700 MHz is the default.
#arm_freq=800

# Uncomment some or all of these to enable the optional hardware interfaces
dtparam=i2c_arm=on
dtparam=i2c1=on

#dtparam=i2s=on
#dtparam=spi=on

# Uncomment this to enable infrared communication.
#dtoverlay=gpio-ir,gpio_pin=17
#dtoverlay=gpio-ir-tx,gpio_pin=18

# Additional overlays and parameters are documented /boot/overlays/README

# Enable audio (loads snd_bcm2835)
dtparam=audio=on

[pi4]
# Enable DRM VC4 V3D driver on top of the dispmanx display stack
dtoverlay=vc4-fkms-v3d
max_framebuffers=2

[all]
#dtoverlay=vc4-fkms-v3d


#iMac G3 settings
hdmi_group=2
hdmi_mode=18
#hdmi_ignore_edid=0xa5000080
#hdmi_force_mode=1
#config_hdmi_boost=7
enable_uart=1

I'm very interested to see this working with a raspberry pi4.

Good luck!
[automerge]1581687419[/automerge]

Hello, long time listener, first time commenter! Been following this thread for months and was excited to see a breakthrough, thank you for all of the work you have put into this! I have hooked my iMac up with a Raspberry Pi 4 and have been able to get everything going except for getting the actual screen on. I can load the init_ivad.py script through SSH and it will turn the screen on, but immediately turn off after about two seconds. Rebooting the Pi will also turn the screen on, but immediately turn it off as well. Nothing shows on the screen when it is on, but I can hear the "click". I have tried pressing keys on the Pi keyboard but it does not seem to be triggering the screen. Any idea what could be going on? Thanks again!

This is probably wishful thinking but maybe the setting are being applied to the other HDMI port.
Try plugging the converter to the other HDMI port and reboot the pi.

I think with a little back and forth we'll get this up and running.

 

[pucher]

Sounds like your almost there!

A couple of questions just to make sure.

1 - Was the iMac working before you pulled the logic board?
2 - Are you jumpering pins 10 and 6 on the J20 connector ?
3 - Have you tested the HDMI to VGA converter separately with another monitor?
4 - Have you confirmed that the VGA cable is wired correctly? If you used the colors
I posted as a guide to splice into your cable make sure thye match up with the pins.
Apple might have changed the wire colors around to keep things lively.
5 - Did you add the lines to the /boot/config.txt file? Specifically
hdmi_group=2
hdmi_mode=18
6 - Do you have a raspberry pi 3 to test with before jumping to the RPI4?

I'm sure you did all of that but I just want to be thorough.

I did this with a Raspberry pi 3 so maybe the difference is there.

There might be an option or two that you'll need for the RPI 4 that I'm not aware of so read through the following.

https://www.raspberrypi.org/documentation/configuration/config-txt/video.md


I see you that you can specify which HDMI port to apply the options to.




Here's a copy of the config.txt file from my pi , maybe I missed something. Let me know if you find that I missed
something and I'll add it to the instructions.

# For more options and information see
# http://rpf.io/configtxt
# Some settings may impact device functionality. See link above for details

# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1

# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
#disable_overscan=1

# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
#overscan_left=16
#overscan_right=16
#overscan_top=16
#overscan_bottom=16

# uncomment to force a console size. By default it will be display's size minus
# overscan.
#framebuffer_width=1280
#framebuffer_height=720

# uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
#hdmi_group=1
#hdmi_mode=1

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL
#sdtv_mode=2

#uncomment to overclock the arm. 700 MHz is the default.
#arm_freq=800

# Uncomment some or all of these to enable the optional hardware interfaces
dtparam=i2c_arm=on
dtparam=i2c1=on

#dtparam=i2s=on
#dtparam=spi=on

# Uncomment this to enable infrared communication.
#dtoverlay=gpio-ir,gpio_pin=17
#dtoverlay=gpio-ir-tx,gpio_pin=18

# Additional overlays and parameters are documented /boot/overlays/README

# Enable audio (loads snd_bcm2835)
dtparam=audio=on

[pi4]
# Enable DRM VC4 V3D driver on top of the dispmanx display stack
dtoverlay=vc4-fkms-v3d
max_framebuffers=2

[all]
#dtoverlay=vc4-fkms-v3d


#iMac G3 settings
hdmi_group=2
hdmi_mode=18
#hdmi_ignore_edid=0xa5000080
#hdmi_force_mode=1
#config_hdmi_boost=7
enable_uart=1

I'm very interested to see this working with a raspberry pi4.

Good luck!
[automerge]1581687419[/automerge]



This is probably wishful thinking but maybe the setting are being applied to the other HDMI port.
Try plugging the converter to the other HDMI port and reboot the pi.

I think with a little back and forth we'll get this up and running.

Yes to all the questions except for 3 and 6. I don't have a Pi 3 on hand to test with, and though I do not have another VGA monitor to test with, the converter cable is brand new from Amazon so I doubt that is the issue. Tried swapping the HDMI port and got the same result, CRT "pop" sound followed by it turning off a few seconds later. Configuration file looks the same to me. Thank you again for the help, anything else I might be able to try?

 

[rockyhill]

Yes to all the questions except for 3 and 6. I don't have a Pi 3 on hand to test with, and though I do not have another VGA monitor to test with, the converter cable is brand new from Amazon so I doubt that is the issue. Tried swapping the HDMI port and got the same result, CRT "pop" sound followed by it turning off a few seconds later. Configuration file looks the same to me. Thank you again for the help, anything else I might be able to try?

Maybe the initialization sequence on your iMac is different, here's something you can try to eliminate
possible initialization sequence problems.

1. Put the logic board and down converter board back in and turn the iMac on with its own power button.
this will initialize the IVAD board.

2. Plug the pi into the spliced video cable and disconnect the SDL and SCL lines from the pi.

3. Turn on the pi.

Hopefully you'll see stuff on the screen

 

[DrJekyll_XYZ]

Yes to all the questions except for 3 and 6. I don't have a Pi 3 on hand to test with, and though I do not have another VGA monitor to test with, the converter cable is brand new from Amazon so I doubt that is the issue. Tried swapping the HDMI port and got the same result, CRT "pop" sound followed by it turning off a few seconds later. Configuration file looks the same to me. Thank you again for the help, anything else I might be able to try?

Are you using a micro HDMI to VGA adapter or a micro HDMI to HDMI to VGA with a few adapters?

Its possible some of the Pins required are not translated between adapters. Check the back of all the TV's in your house and see if they have VGA and just test everything is working. I know you dont have a monitor to hand but that is the best test you can do as a first step.

Which model of iMac is it? there are differences in the late 90's slot load models to the 2001 slot load models. I have a DV model which is different internally from the Bondi Blue slot load.

Maybe the initialization sequence on your iMac is different, here's something you can try to eliminate
possible initialization sequence problems.

1. Put the logic board and down converter board back in and turn the iMac on with its own power button.
this will initialize the IVAD board.

2. Plug the pi into the spliced video cable and disconnect the SDL and SCL lines from the pi.

3. Turn on the pi.

Hopefully you'll see stuff on the screen

Rocky, i dont suppose you know the model of iMac that the initialisation code was taken from?

 

[rockyhill]

Are you using a micro HDMI to VGA adapter or a micro HDMI to HDMI to VGA with a few adapters?

Its possible some of the Pins required are not translated between adapters. Check the back of all the TV's in your house and see if they have VGA and just test everything is working. I know you dont have a monitor to hand but that is the best test you can do as a first step.

Which model of iMac is it? there are differences in the late 90's slot load models to the 2001 slot load models. I have a DV model which is different internally from the Bondi Blue slot load.



Rocky, i dont suppose you know the model of iMac that the initialisation code was taken from?

Good suggestion, hopefully he has a VGA port on his tv.

I don't know which model the code was captured from but I can tell you that my model is an iMac DV
model M5521 and apart from some minor tweaks, sparpet's capture works.

 

[rockyhill]

Hello, long time listener, first time commenter! Been following this thread for months and was excited to see a breakthrough, thank you for all of the work you have put into this! I have hooked my iMac up with a Raspberry Pi 4 and have been able to get everything going except for getting the actual screen on. I can load the init_ivad.py script through SSH and it will turn the screen on, but immediately turn off after about two seconds. Rebooting the Pi will also turn the screen on, but immediately turn it off as well. Nothing shows on the screen when it is on, but I can hear the "click". I have tried pressing keys on the Pi keyboard but it does not seem to be triggering the screen. Any idea what could be going on? Thanks again!

Well, I tried to get this to work with a second iMac G3 DV of the same model but 1 year older and it didn't work........
I sniffed the initialization code and sure enough it's different! Tomorrow I'm going to try and code that sequence and test some more.

 

[rockyhill]

Hello, long time listener, first time commenter! Been following this thread for months and was excited to see a breakthrough, thank you for all of the work you have put into this! I have hooked my iMac up with a Raspberry Pi 4 and have been able to get everything going except for getting the actual screen on. I can load the init_ivad.py script through SSH and it will turn the screen on, but immediately turn off after about two seconds. Rebooting the Pi will also turn the screen on, but immediately turn it off as well. Nothing shows on the screen when it is on, but I can hear the "click". I have tried pressing keys on the Pi keyboard but it does not seem to be triggering the screen. Any idea what could be going on? Thanks again!

So I think I'm having a similar problem with my other iMac G3.

I cannot get it to display anything by sending the new init sequence via arduino or raspberry pi.
However, if I leave the Logic board installed and let it initiate the LVAD board but
send video from my computer, it comes to life.

If you'r using linux and have a computer with a VGA connector you can do the same thing.
If you don't have linux you can probably just download ubuntu 18.04 ,make a live desktop and
run everything from a usb stick. No need to install linux

1 - replace the logic board and re-attach the i2c lines.
2 - connect the vga cable to your linux computer(not raspberry pi).
3 - type "xrandr" to get a list of displays and supported configs.
4 - turn on the iMac
5 - look for something like VGA or VGA1. On my computer it's "VGA-1"
6 - type the following:

xrandr --newmode "1024x768_75.00"  81.80  1024 1080 1192 1360  768 769 772 802  -HSync +Vsync
xrandr --addmode VGA-1 "1024x768_75.00"
xrandr --output VGA-1 --mode "1024x768_75.00"

Replace "VGA-1" with whatever it's called on your computer.

I tried to do the same thing with an HDMI to VGA converter but had no luck. For now I think you would need to test with a rel VGA out.

I think these iMac's have a different "thing" that's done with the PFW and
Line Sense lines, we just have to see what needs to be done for them to stay on.

 

[DrJekyll_XYZ]

So I think I'm having a similar problem with my other iMac G3.

I cannot get it to display anything by sending the new init sequence via arduino or raspberry pi.
However, if I leave the Logic board installed and let it initiate the LVAD board but
send video from my computer, it comes to life.

If you'r using linux and have a computer with a VGA connector you can do the same thing.
If you don't have linux you can probably just download ubuntu 18.04 ,make a live desktop and
run everything from a usb stick. No need to install linux

1 - replace the logic board and re-attach the i2c lines.
2 - connect the vga cable to your linux computer(not raspberry pi).
3 - type "xrandr" to get a list of displays and supported configs.
4 - turn on the iMac
5 - look for something like VGA or VGA1. On my computer it's "VGA-1"
6 - type the following:

xrandr --newmode "1024x768_75.00"  81.80  1024 1080 1192 1360  768 769 772 802  -HSync +Vsync
xrandr --addmode VGA-1 "1024x768_75.00"
xrandr --output VGA-1 --mode "1024x768_75.00"

Replace "VGA-1" with whatever it's called on your computer.

I tried to do the same thing with an HDMI to VGA converter but had no luck. For now I think you would need to test with a rel VGA out.

I think these iMac's have a different "thing" that's done with the PFW and
Line Sense lines, we just have to see what needs to be done for them to stay on.

As I have a RPI free and not an Arduino, I will try to replicate what you're doing with my iMac DV to see if the init code works when I get some free time... Have you uploaded the second init script to your GitHub just in case? We may end up building a repository of them to make things work for others at this rate... I'll find a way to use the pi to sniff my code see if it differs from yours

 

[RainbowAsteroids]

Before I try this project, I just wanna verify that all that was accomplished here only applies to the slot-loading iMac, because I have a tray-loading fruit G3.

 

[rockyhill]

As I have a RPI free and not an Arduino, I will try to replicate what you're doing with my iMac DV to see if the init code works when I get some free time... Have you uploaded the second init script to your GitHub just in case? We may end up building a repository of them to make things work for others at this rate... I'll find a way to use the pi to sniff my code see if it differs from yours

I just added the second init script , arduino & python, to the repo.
https://github.com/qbancoffee/imac_g3_ivad_board_init

might have to come up with a better name......

I agree, it looks like we're going to have a collection of these init sequences but I bet we can make it all work in a
single script. Somehow we have to figure out a way to differentiate between the different iMac DV's....

Now that you are going to sniff with a pi,
I think we should also come up with a standardized way of sniffing the sequence and document it.
That way it's a recipe that's somewhat easy to follow. I think we can then write a python script that can take that sniffed
sequence and produce the init scripts automatically.
[automerge]1581913897[/automerge]

Before I try this project, I just wanna verify that all that was accomplished here only applies to the slot-loading iMac, because I have a tray-loading fruit G3.

So far I've been only working with slot-loading iMac's and an eMac but Stephen Ferris has done it with a
tray loader. He says that no init sequence is necessary, just a DB15 to DE15 cable adapter.
[automerge]1581914150[/automerge]
I was able to make my other iMac work with the new init sequence, an arduino and no logic board.
It was a combination of PFW, Trickle LineSense and LP. I've done it a hand full of times but I don't have
the sequence down yet but hopefully soon I will.

One thing's for sure though, 5VTrickle and PFW have to be shorted the whole time. You can't just touch them for
two seconds like my other iMac.........

 

[DrJekyll_XYZ]

Now that you are going to sniff with a pi,
I think we should also come up with a standardized way of sniffing the sequence and document it.
That way it's a recipe that's somewhat easy to follow. I think we can then write a python script that can take that sniffed
sequence and produce the init scripts automatically.

We could use piscope to do this however it has a maximum of 100kbps i2c bus otherwise it wont reliably read. Do you know what rate the imac uses?